linux-stable.git/net/ipv4/tcp_input.c, branch linux-rolling-lts Linux kernel stable tree tcp: fix stale per-CPU tcp_tw_isn leak enabling ISN prediction 2026-06-01T15:51:06+00:00 Eric Dumazet edumazet@google.com 2026-05-19T08:46:11+00:00 e47f7060eaf60894e3e4d0e3c4fe6e1f2eacfbdd [ Upstream commit 1bbf0ced1d9db73ac7893c2187f3459288603e0d ] Blamed commit moved the TIME_WAIT-derived ISN from the skb control block to a per-CPU variable, assuming the value would always be consumed by tcp_conn_request() for the same packet that wrote it. That assumption is violated by multiple drop paths between the producer (__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer (tcp_conn_request()): - min_ttl / min_hopcount check - xfrm policy check - tcp_inbound_hash() MD5/AO mismatch - tcp_filter() eBPF/SO_ATTACH_FILTER drop - th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN - psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv() - tcp_checksum_complete() in tcp_v{4,6}_do_rcv() - tcp_v{4,6}_cookie_check() returning NULL When a packet is dropped on any of these paths, tcp_tw_isn is left set. The next SYN processed on the same CPU then consumes the non zero value in tcp_conn_request(), receiving a potentially predictable ISN. This patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu variable. Note that tcp_v{4,6}_fill_cb() do not set it. Very litle impact on overall code size/complexity: $ scripts/bloat-o-meter -t vmlinux.old vmlinux.new add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7) Function old new delta tcp_v6_rcv 3038 3042 +4 tcp_v4_rcv 3035 3039 +4 tcp_conn_request 2938 2923 -15 Total: Before=24436060, After=24436053, chg -0.00% Fixes: 41eecbd712b7 ("tcp: replace TCP_SKB_CB(skb)->tcp_tw_isn with a per-cpu field") Reported-by: Chris Mason <clm@meta.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com> Link: https://patch.msgid.link/20260519084611.2485277-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 1bbf0ced1d9db73ac7893c2187f3459288603e0d ]

Blamed commit moved the TIME_WAIT-derived ISN from the skb control
block to a per-CPU variable, assuming the value would always be consumed
by tcp_conn_request() for the same packet that wrote it. That assumption
is violated by multiple drop paths between the producer
(__this_cpu_write(tcp_tw_isn, isn) in tcp_v{4,6}_rcv()) and the consumer
(tcp_conn_request()):

 - min_ttl / min_hopcount check
 - xfrm policy check
 - tcp_inbound_hash() MD5/AO mismatch
 - tcp_filter() eBPF/SO_ATTACH_FILTER drop
 - th->syn && th->fin discard in tcp_rcv_state_process() TCP_LISTEN
 - psp_sk_rx_policy_check() in tcp_v{4,6}_do_rcv()
 - tcp_checksum_complete() in tcp_v{4,6}_do_rcv()
 - tcp_v{4,6}_cookie_check() returning NULL

When a packet is dropped on any of these paths, tcp_tw_isn is left set.

The next SYN processed on the same CPU then consumes the non zero value in
tcp_conn_request(), receiving a potentially predictable ISN.

This patch moves back tcp_tw_isn to skb->cb[], getting rid of the per-cpu
variable.

Note that tcp_v{4,6}_fill_cb() do not set it.

Very litle impact on overall code size/complexity:

$ scripts/bloat-o-meter -t vmlinux.old vmlinux.new
add/remove: 0/0 grow/shrink: 2/1 up/down: 8/-15 (-7)
Function                                     old     new   delta
tcp_v6_rcv                                  3038    3042      +4
tcp_v4_rcv                                  3035    3039      +4
tcp_conn_request                            2938    2923     -15
Total: Before=24436060, After=24436053, chg -0.00%

Fixes: 41eecbd712b7 ("tcp: replace TCP_SKB_CB(skb)->tcp_tw_isn with a per-cpu field")
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260519084611.2485277-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: send a challenge ACK on SEG.ACK > SND.NXT 2026-05-23T11:07:05+00:00 Jiayuan Chen jiayuan.chen@linux.dev 2026-04-22T12:35:38+00:00 671f743d2dd50a36b33f485ac2a745f0ecde3d72 [ Upstream commit 42726ec644cbdde0035c3e0417fee8ed9547e120 ] RFC 5961 Section 5.2 validates an incoming segment's ACK value against the range [SND.UNA - MAX.SND.WND, SND.NXT] and states: "All incoming segments whose ACK value doesn't satisfy the above condition MUST be discarded and an ACK sent back." Commit 354e4aa391ed ("tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation") opted Linux into this mitigation and implements the challenge ACK on the lower side (SEG.ACK < SND.UNA - MAX.SND.WND), but the symmetric upper side (SEG.ACK > SND.NXT) still takes the pre-RFC-5961 path and silently returns SKB_DROP_REASON_TCP_ACK_UNSENT_DATA, even though RFC 793 Section 3.9 (now RFC 9293 Section 3.10.7.4) has always required: "If the ACK acknowledges something not yet sent (SEG.ACK > SND.NXT) then send an ACK, drop the segment, and return." Complete the mitigation by sending a challenge ACK on that branch, reusing the existing tcp_send_challenge_ack() path which already enforces the per-socket RFC 5961 Section 7 rate limit via __tcp_oow_rate_limited(). FLAG_NO_CHALLENGE_ACK is honoured for symmetry with the lower-edge case. Update the existing tcp_ts_recent_invalid_ack.pkt selftest, which drives this exact path, to consume the new challenge ACK. Fixes: 354e4aa391ed ("tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation") Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260422123605.320000-2-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 42726ec644cbdde0035c3e0417fee8ed9547e120 ]

RFC 5961 Section 5.2 validates an incoming segment's ACK value
against the range [SND.UNA - MAX.SND.WND, SND.NXT] and states:

  "All incoming segments whose ACK value doesn't satisfy the above
   condition MUST be discarded and an ACK sent back."

Commit 354e4aa391ed ("tcp: RFC 5961 5.2 Blind Data Injection Attack
Mitigation") opted Linux into this mitigation and implements the
challenge ACK on the lower side (SEG.ACK < SND.UNA - MAX.SND.WND),
but the symmetric upper side (SEG.ACK > SND.NXT) still takes the
pre-RFC-5961 path and silently returns
SKB_DROP_REASON_TCP_ACK_UNSENT_DATA, even though RFC 793 Section 3.9
(now RFC 9293 Section 3.10.7.4) has always required:

  "If the ACK acknowledges something not yet sent (SEG.ACK > SND.NXT)
   then send an ACK, drop the segment, and return."

Complete the mitigation by sending a challenge ACK on that branch,
reusing the existing tcp_send_challenge_ack() path which already
enforces the per-socket RFC 5961 Section 7 rate limit via
__tcp_oow_rate_limited().  FLAG_NO_CHALLENGE_ACK is honoured for
symmetry with the lower-edge case.

Update the existing tcp_ts_recent_invalid_ack.pkt selftest, which
drives this exact path, to consume the new challenge ACK.

Fixes: 354e4aa391ed ("tcp: RFC 5961 5.2 Blind Data Injection Attack Mitigation")
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260422123605.320000-2-jiayuan.chen@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: annotate data-races around tp->srtt_us 2026-05-23T11:07:01+00:00 Eric Dumazet edumazet@google.com 2026-04-16T20:03:16+00:00 0edffaf11267c84d9c285886ec591da9f1d83faf [ Upstream commit 290b693ce7c9d48588d88b15a782a3efc6fa036b ] tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy. Fixes: e8bd8fca6773 ("tcp: add SRTT to SCM_TIMESTAMPING_OPT_STATS") Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260416200319.3608680-12-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 290b693ce7c9d48588d88b15a782a3efc6fa036b ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy.

Fixes: e8bd8fca6773 ("tcp: add SRTT to SCM_TIMESTAMPING_OPT_STATS")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-12-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: better handle TCP_TX_DELAY on established flows 2026-05-23T11:07:01+00:00 Eric Dumazet edumazet@google.com 2025-10-13T14:59:26+00:00 cd6011dc4c339b83a853901d9772e8e07927ddc3 [ Upstream commit 1c51450f1afff1e7419797720df3fbd9ccbf610c ] Some applications uses TCP_TX_DELAY socket option after TCP flow is established. Some metrics need to be updated, otherwise TCP might take time to adapt to the new (emulated) RTT. This patch adjusts tp->srtt_us, tp->rtt_min, icsk_rto and sk->sk_pacing_rate. This is best effort, and for instance icsk_rto is reset without taking backoff into account. Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20251013145926.833198-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Stable-dep-of: 290b693ce7c9 ("tcp: annotate data-races around tp->srtt_us") Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 1c51450f1afff1e7419797720df3fbd9ccbf610c ]

Some applications uses TCP_TX_DELAY socket option after TCP flow
is established.

Some metrics need to be updated, otherwise TCP might take time to
adapt to the new (emulated) RTT.

This patch adjusts tp->srtt_us, tp->rtt_min, icsk_rto
and sk->sk_pacing_rate.

This is best effort, and for instance icsk_rto is reset
without taking backoff into account.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20251013145926.833198-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 290b693ce7c9 ("tcp: annotate data-races around tp->srtt_us")
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: annotate data-races around tp->reord_seen 2026-05-23T11:07:01+00:00 Eric Dumazet edumazet@google.com 2026-04-16T20:03:15+00:00 3955bfec74ab41925252951f2364fb7e4c2b2752 [ Upstream commit 62585690e6b2a112c408fe25f142b246ac833c42 ] tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy. Fixes: 7ec65372ca53 ("tcp: add stat of data packet reordering events") Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260416200319.3608680-11-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 62585690e6b2a112c408fe25f142b246ac833c42 ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy.

Fixes: 7ec65372ca53 ("tcp: add stat of data packet reordering events")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-11-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: annotate data-races around tp->dsack_dups 2026-05-23T11:07:00+00:00 Eric Dumazet edumazet@google.com 2026-04-16T20:03:14+00:00 7fc9ef56acfe9d74f8d73b5a8b130200a37bcccb [ Upstream commit a984705ca88b976bf1087978fd98b7f3993da88c ] tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy. Fixes: 7e10b6554ff2 ("tcp: add dsack blocks received stats") Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260416200319.3608680-10-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit a984705ca88b976bf1087978fd98b7f3993da88c ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy.

Fixes: 7e10b6554ff2 ("tcp: add dsack blocks received stats")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-10-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: add data-race annotations for TCP_NLA_SNDQ_SIZE 2026-05-23T11:07:00+00:00 Eric Dumazet edumazet@google.com 2026-04-16T20:03:11+00:00 5987cec30473c58f29df33625b9270ce2e5d88f6 [ Upstream commit 124199444de467767175a9004e1574dc42523e62 ] tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy. Fixes: 87ecc95d81d9 ("tcp: add send queue size stat in SCM_TIMESTAMPING_OPT_STATS") Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260416200319.3608680-7-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 124199444de467767175a9004e1574dc42523e62 ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy.

Fixes: 87ecc95d81d9 ("tcp: add send queue size stat in SCM_TIMESTAMPING_OPT_STATS")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-7-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: annotate data-races around tp->delivered and tp->delivered_ce 2026-05-23T11:07:00+00:00 Eric Dumazet edumazet@google.com 2026-04-16T20:03:10+00:00 4215a5c7b07981fcb5c59470797f4d0e8718474e [ Upstream commit faa886ad3ce5fc8f5156493491fe189b2b726bc9 ] tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy. Fixes: feb5f2ec6464 ("tcp: export packets delivery info") Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260416200319.3608680-6-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit faa886ad3ce5fc8f5156493491fe189b2b726bc9 ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy.

Fixes: feb5f2ec6464 ("tcp: export packets delivery info")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: annotate data-races around tp->snd_ssthresh 2026-05-23T11:07:00+00:00 Eric Dumazet edumazet@google.com 2026-04-16T20:03:09+00:00 d8068252f0435938ccb36e24e9c07475e5dff381 [ Upstream commit fd571afb05ebaeac5d8f09460a0640d4cf6755f8 ] tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy. Fixes: 7156d194a077 ("tcp: add snd_ssthresh stat in SCM_TIMESTAMPING_OPT_STATS") Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260416200319.3608680-5-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit fd571afb05ebaeac5d8f09460a0640d4cf6755f8 ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE() and WRITE_ONCE() annotations to keep KCSAN happy.

Fixes: 7156d194a077 ("tcp: add snd_ssthresh stat in SCM_TIMESTAMPING_OPT_STATS")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
tcp: add data-races annotations around tp->reordering, tp->snd_cwnd 2026-05-23T11:07:00+00:00 Eric Dumazet edumazet@google.com 2026-04-16T20:03:08+00:00 9bce4d9c6da13991d84e2dc1711f09cd39e4df02 [ Upstream commit 829ba1f329cb7cbd56d599a6d225997fba66dc32 ] tcp_get_timestamping_opt_stats() intentionally runs lockless, we must add READ_ONCE(), WRITE_ONCE() data_race() annotations to keep KCSAN happy. Fixes: bb7c19f96012 ("tcp: add related fields into SCM_TIMESTAMPING_OPT_STATS") Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260416200319.3608680-4-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> 
[ Upstream commit 829ba1f329cb7cbd56d599a6d225997fba66dc32 ]

tcp_get_timestamping_opt_stats() intentionally runs lockless, we must
add READ_ONCE(), WRITE_ONCE() data_race() annotations to keep KCSAN happy.

Fixes: bb7c19f96012 ("tcp: add related fields into SCM_TIMESTAMPING_OPT_STATS")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260416200319.3608680-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>